Drive system for mechanical filter



May 24, 1955 D- F. BABcocK 2,799,243

DRIVE SYSTEM FOR MECHANICAL FILTER Filed May 16, 1952 2 Sheets-Sheet lIN VEN TOR.

BA /m if. 19/09 0001:

\ATTOYJE'IVIY May 24, 1.955 D. F. BABCOCK DRIVE SYSTEM FOR MECHANICALFILTER 2 Sheets-Sheet 2 Filed May 16, 1952 5'22 af/TY Arron/wry UnitedStates Patent DRIVE SYSTEM FOR MECHANICAL FILTER Dean F. Babcock,Burbank, Califi, assignor to Collins Radio Company, Cedar Rapids, Iowa,a corporation of Iowa Application May 16, 1952, Serial No. 288,349

4 Claims. (Cl. 33371) This invention relates in general toelectromagnetic filters and in particular to an improvedmagnetostrictive driving means.

The co-pending application of Melvin L. Doelz entitled MechanicalFilters, filed September 24, 1951, Serial Number 248,011, discloses anelectromechanical filter wherein a plurality of discs are attachedtogether by longitudinal connecting wires and energy is coupled to andremoved from opposite end discs by input and output driving wires. Thedriving wires are coupled to input and output coils. Applicant hasdiscovered that the coupling between a magnetostrictive wire and amagnetic driving means may be increased appreciably by using a pluralityof driving coils strategically spaced relative to the wire.

It is an object of this invention, therefore, to provide an improved,more efficient driving system for a magnetostrictive coupling.

Another object of this invention is to provide an improvedmagnetostrictive coupling means which utilizes a plurality of coilscoupled to a magnetostrictive wire with adjoining coils wound in buckingfashion.

A feature of this invention is found in the provision for mounting aplurality of driving coils relative to a magnetostrictive wire atpositions which increase the efiiciency of the coupling between thecoils and the wire.

Further features, objects and advantages of this invention will becomeapparent from the following description and claims when read in view ofthe drawings, in which;

Figure 1 is a side view of an electromechanical filter showing the coverplate in section so as to illustrate the internal construction;

Figure 2a is a sectional view of the coupling means of theelectromechanical filter shown in Figure 1;

Figure 2b is a plot of velocity versus position along the driving wireshown in Figure 2a;

Figure 3 is a sectional view of a modification of the coupling meansshown in Figure 1; and,

Figure 4 is an end view of the coupling means of Figure 1.

Figure 1 illustrates an electromechanical filter wherein a base platehas a pair of stand-offs 11 and 12 mounted thereon. A pair of hollowcylinders 13 and 14 pass through the stand-offs 11 and 12 and aresupported thereby. End discs 16 and 17, respectively, are attached tothe cylinders 13 and 14 by welding.

A plurality of active discs 18 are supported between the end discs 16and 17 by longitudinal supporting wires 19. The active discs adjacentthe end discs 16 and 17 have output and input driving wires 21 and 22,respectively, attached thereto. The driving wires 21 and 22 extendwithin the confines of the cylinders 13 and 14 and pass through magneticdriving and output means mounted in these coils.

A pair of input leads 23 and 24, respectively, extend from the cylinder13 and are attached to terminals 26 which extend through the base plate10. Similarly, a pair of output leads 27 and 28 extend from the cylinder14 and are attached to terminals 29 which extend through the base plate10. It is to be realized that there are two each of contacts 26 and 29.

Mounting pins 31 and 32 are attached to the base plate 10 and may beused for attaching the filter to a chassis. A cover member 33 isgenerally rectangular in shape and is welded or crimped to the baseplate 10 so as to form a cover for the filter.

Polarizing magnets 34 and 35, respectively, are mounted to thestand-offs 11 and 12 adjacent the cylinders 13 and 14. The cylinders 13and 14 may be made of brass or any other suitable non-magnetic material.

This invention relates to an improvement in the magnetostrictivecoupling means which are contained in the cylinders 13 and 14.Previously, the cylinder 13 has contained a single driving coil which ismounted concentric about the magnetostrictive wire 21 to excite it witha driving signal.

Figure 2a is a sectional view taken through the cylinder 13 andillustrates the magnetostrictive wire 21 extending therethrough. It isto be noted that the disc 16 has a portion removed adjacent its loweredge so that the wire 21 does not touch it. Within the confines ofcylinder 13 are mounted a pair of driving coils 36 and 37, respectively,which are held in place by suitable rings 38, 39, 41 and 42,respectively.

The start wire 23 is connected to the coil 36 and the finish Wire 43 ofthe coil 36 is attached to coil 37. The output wire 24 is connected tothe opposite end of the coil 37. It is to be noted that coils 36 and 37are wound in opposite directions so that the flux produced by the coilswill buck each other.

Figure 2b illustrates the spacing of the coils 36 and 37 relative to thewire 21. The axis of ordinates shows the velocity of a point on the wire21 when being driven and the axis of abscissas corresponds to distancealong the wire 21. It is to be realized that the curve of Figure 2b is adynamic curve. It is to be noted that the length of the wire 21 from itsfree end to the disc 18 is wave lengths and that velocity nodes arelocated at and 7,, wave lengths from the free end.

It is to be realized, of course, that velocity nodes correspond topoints of maximum stress in the wire 21. The coils 36 and 37 are mountedimmediately below points A and B, respectively, which correspond to thevelocity nodes of the wire 21. Thus, the coil 36 is spaced wave lengthfrom the free end of the wire 21 and the coil 37 is placed wave lengthfrom the free end of the wire. The wave length corresponds to theresonant frequency of the filter which is determined by the length ofthe wire and the physical characteristics of the discs 18.

The advantages obtained by using a pair of coils 36 and 37 connected inseries opposition over a single driving coil is due primarily to theinternal friction of the magnetostrictive wire which causes vibrationsset up at one point of the wire to decrease exponentially as thedistance increases from the driving point. By driving in oppositefashion at two points, such as shown in Figure 2a, a more efficient orcloseness of coupling is obtained.

It is analogous to pushing a child in a swing, wherein a man standing onone side and giving the swing a push each time it returns will expendmore energy than the total of two men standing on opposite sides of theswing and giving it a push each time it returns. This is assuming thatthe swing maintains a fixed maximum amplitude. Thus, the same amount ofenergy applied to two points along the wire 21 will cause greater vi- Vbration of the disc 18 than when the energy is applied at one point.

A modification of this invention is shown in Figure 3 where the coils 36and 37 have been surrounded by magnetic material 44, as for example,pressed. powdered iron. The magnetic material 44 may be divided into twoparts to form half-cylinders, 46 and 47, as best shown in Figure 4, sothat they may be assem bled with the coils 35 and 37 and mounted incylinders 13.

The magnetic material 44 is formed with three projections 48, 49 and 51that extend down toward the wire 21 between and. at either side of coils36 and 37. The coils 36 and 37 are connected in bucking fashion. Theaction of the structure shown in Figure 3 is in all ways the same asthat shown in Figure 2a except that the higher permeability of the mediaachieved by the magnetic material shown in Figure 3 increases stillfurther the closeness of coupling between the electrical and mechanicalelements by increasing the amount of flux in the driving wires for agiven current flowing through the coupling coils.

It is seen that this invention provides means for driving amagnetostrictive wire at a plurality of points so as to obtain anincreased etficiency.

Although this invention has been described with respect to particularembodiments thereof, it is not to be so limited as changes andmodifications may be made therein which are within the full intendedscope of the invention, as defined by the appended claims.

I claim:

1. An exciter system for an electromechanical resonator comprising, acoupling wire with a free end and an attached end connected to saidresonator, a pair of coils mounted concentric about said coupling wire,the first coil mounted one quarter wave length at the resonant frequencyof the resonator from, the free end of the coupling wire, the other coilmounted three quarter wave lengths at the resonant frequency of theresonator from the free end of the wire, and said first and second coilsconnected together in bucking fashion.

2. An electromechanical coupling means for coupling energy between amagnetostrictive coupling wire with a free end and an attached end and aplurality of coils comprising, supporting means, a mechanical resonatingsystem, supporting wires extending from Said supporting means andconnected to said resonating system, the attached end of saidmagnetostrictive coupling wire connected to said mechanical resonatingsystem, a pair of electromagnetic coils mounted concentric about saidcoupling wire, the first coil mounted one quarter wave length of theresonant frequency of the mechanical system from the free end, and thesecond coil mounted three quarter wave lengths of the resonant frequencyof the mechanical system from the free end.

3. Means for erficiently coupling energy between magnetic means and amagnetostrictive coupling wire which is connected to a mechanicalvibrating system comprising, a pair of coils connected together inbucking fashion and mounted concentric about said coupling wire, agenerally cylindrical shaped flux conducting means mounted about saidcoupling wire and said first and second coils, and portions of said fluxconducting means extending inwardly closely adjacent said coupling wireintermediate said coils and at either side thereof.

4. Means for eificiently coupling energy to and from a magnetostrictivewire comprising, a pair of coupling coils mounted concentrically aboutsaid wire, magnetic material mounted concentric about said Wire andbetween the coupling coils, portions of said magnetic material extendingclosely adjacent said coupling wire, and said coils mounted at velocitynodal points along said wire.

References Cited in the file of this patent UNITED STATES PATENTS2,167,078 Lakatos July 25, 1939 2,490,273 Kean Dec. 6,, 1949 2,526,229Hazeltine Oct 17, 1950 FOREIGN PATENTS 633,429 Great Britain Dec. 19,1949

